The present invention relates to light strings having light units arranged in series.
Decorative light strings are highly popular in the United States, especially during November and December, in celebration of Christmas. Such light strings are typically used to decorate houses and business buildings, both indoors and outdoors, as well as trees, bushes, and yard ornaments. Indeed, it is reasonable to say that most, if not all, Americans have used decorative light strings in or around their homes, or at least certainly seen them aglow in numerous decorative lighting arrangements in all sorts of settings during the xe2x80x9choliday season.xe2x80x9d
Decorative light strings are commonly comprised of a plurality of individual light units with miniature bulbs, electrically connected in series. The miniature bulbs are typically incandescent bulbs, and as such, each has a filament formed between two leads of the bulb, the filament giving off light when a current is passed from one lead to the other, through the filament. As the bulb is used, over time, the filament will burn out, breaking the series circuit in which the bulb is arranged. This will cause the entire light string to go out unless a backup circuit path is available to bypass the failed filament.
To provide a backup circuit path, some decorative light strings are manufactured with bulbs having a shunt arranged in parallel with the filament of each bulb, both the shunt and filament being disposed between the two leads of the bulb. These shunts can be comprised of a conducting material with an insulating coating. When the filament is intact, current passes therethrough because the resistance of the filament is low compared to that of the insulating material on the shunt. However, when the filament burns out, the voltage across the leads of the bulb drives current across the shunt, burning off the insulating material of the shunt, and allowing it to conduct electricity between the two leads of the bulb, thereby providing a backup circuit path around the failed filament. In this manner, even if a bulb burns out, the rest of the light units in the light string remain on because the series circuit remains closed.
Despite the availability of decorative light strings having bulbs with shunts, problems still persist related to maintaining a complete circuit in the light strings. For example, although such light strings provide an alternate circuit path (i.e. a parallel shunt) when a bulb burns out, if the bulb itself is destroyed, removed or loose such that its leads are not in contact with the main conducting wire of the circuit, then the current path to both the shunt and filament are broken, and hence, the entire series circuit of the light string is broken. A user may then have to manually inspect each and every bulb of a light string to check if it is properly installed before being able to complete the circuit and restore the light string to working order. This problem arises so frequently that testing devices are reportedly sold to test for loose bulbs when a light string is not working properly. Also, the shunt of a bulb could be defective for various reasons, in which case, no backup circuit path is available when the bulb burns out. Again, this can result in the entire light string being inoperable and the user having to individually inspect each and every bulb of the light string to determine which bulb has failed, or is defective, and otherwise needs replacement.
The problems discussed above limit reliability of decorative light strings and result in significant inconvenience and hassle to users. There is a need for a more reliable design for decorative light strings that eliminates or significantly reduces the frequency with which they must be inspected and maintained.
One embodiment of the present invention comprises a light unit for use with a light string having at least two light units connected in series. Each light unit includes a socket unit, or connection unit, that is connected to separate wire segments via contact elements. The wire segments make up the wire of the light string. A bulb assembly is receivable by the socket unit and can be removed and replaced when a filament of the bulb assembly burns out.
There is a mechanical switch in the socket unit that is operable between a closed position for providing a circuit path between the separate wire segments and an open position wherein the circuit path is broken. When the switch is closed, the circuit path provided by the switch is parallel to a circuit path through the bulb assembly of the light unit.
The bulb assembly has an actuating member that impinges against a moveable member of the switch to displace the switch from the closed position to the open position when the bulb assembly is received by the socket unit. The switch has a biasing component with a restoring force that repositions the switch from the open position to the closed position when the bulb assembly is removed or loosened from the socket unit.
In some embodiments, a shunt assembly is also provided that can be inserted within the socket unit, between the contact elements of the socket unit. The shunt assembly has a high resistance element and a non-conducting retainer. The retainer is made of an elastic (resilient) material to provide a restoring force when bent, and the high resistance element is attached to the retainer. The retainer is configured so that at least a portion thereof must be deformed against its restoring force in order to fit the retainer within the socket unit. The high resistance element is positioned on the retainer such when the retainer is inserted in the socket unit, the high resistance element is disposed between the retainer and the contact elements, with the restoring force of the retainer urging the high resistance element against the contact elements.
The present invention also includes embodiments of light strings having light units of various embodiments, including the embodiments disclosed above. Also, methods of operating light strings are provided. Some embodiments of such methods comprise passing current through a filament of a bulb to generate light until the filament fails and then removing the bulb from the light string to restore power to another light unit within the light string. In yet another embodiment, current is passed through a filament of a bulb until the filament fails, then passed through a primary shunt. The bulb is then replaced without replacing a secondary shunt, which is reused as a backup shunt.